Dimensionally stable electrodes are comprised of particulates fabricated from nitrides of metals selected from the IV B and V B groups. These electrodes are designed for use in bipolar electrolytic cells. Bipolar cells are used to remove ions from solution in such applications as metal recover processes and water purification.
Bipolar electrolytic cells have been used for many years in electrochemical processes. In these cells particles of an electrically-conductive material act as both anodes and cathodes. In this manner, the electrical resistance of the cell is reduced and overall efficiency is improved.
A significant advancement in bipolar cells was disclosed in U.S. Pat. No. 6,391,186 issued May 21, 2002. The unique feature of this improvement is the use of an intimate mixture of electrically conductive and non-conductive particles spaced between two electrical leads. The conductive particles form clumps or strands that act as bipolar electrodes.
Notwithstanding the advantages of the improved bipolar cell, practical considerations limit its use. All of the materials so far considered for use in the electrically-conductive particles have drawbacks. Carbonaceous substances including graphite are attacked in many applications. Platinum, even when employed for plating a substrate, is expensive. And lead, also mentioned in the literature, has the decided disadvantage of being toxic.
Therefore, it is an object of the present invention to provide bipolar electrodes that have none of the disadvantages of those proposed in the prior art. These goals and other objects, features and advantages of the invention will be apparent from the accompanying drawing and the following description.
The present invention discloses dimensionally stable electrodes for use in bipolar electrolytic cells. These dimensionally stable electrodes are comprised of particulates fabricated from nitrides of metals selected from the groups IV B and V B. These particulates, which are electrically conductive, are intimately mixed with non-conductive particulates, and the mixture is spaced between two electrical leads to provide a bipolar cell.
The metallic nitrides formed from metals of groups IV B and V B include titanium nitride, zirconium nitride, hafnium nitride, vanadium nitride, niobium nitride and tantalum nitride. These nitrides may be used in their pure form or as complexes of two or more nitrides. Because of the refractory nature of the metallic nitrides, shapes of these materials commonly are formed by hot pressing or pressure sintering of the powdered substance. The metallic nitride, however, need not be used in a monolithic particulate, but it can be applied as a coating to a substrate.